/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core;

import org.springframework.lang.Nullable;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;

/**
 * Internal utility class that can be used to obtain wrapped {@link Serializable}
 * variants of {@link java.lang.reflect.Type java.lang.reflect.Types}.
 *
 * <p>{@link #forField(Field) Fields} or {@link #forMethodParameter(MethodParameter)
 * MethodParameters} can be used as the root source for a serializable type.
 * Alternatively, a regular {@link Class} can also be used as source.
 *
 * <p>The returned type will either be a {@link Class} or a serializable proxy of
 * {@link GenericArrayType}, {@link ParameterizedType}, {@link TypeVariable} or
 * {@link WildcardType}. With the exception of {@link Class} (which is final) calls
 * to methods that return further {@link Type Types} (for example
 * {@link GenericArrayType#getGenericComponentType()}) will be automatically wrapped.
 *
 * @author Phillip Webb
 * @author Juergen Hoeller
 * @since 4.0
 */
final class SerializableTypeWrapper
{

    static final         ConcurrentReferenceHashMap<Type, Type> cache                        = new ConcurrentReferenceHashMap<>(256);
    private static final Class<?>[]                             SUPPORTED_SERIALIZABLE_TYPES = {GenericArrayType.class, ParameterizedType.class, TypeVariable.class, WildcardType.class};


    private SerializableTypeWrapper()
    {
    }


    /**
     * Return a {@link Serializable} variant of {@link Field#getGenericType()}.
     */
    @Nullable
    public static Type forField(Field field)
    {
        return forTypeProvider(new FieldTypeProvider(field));
    }

    /**
     * Return a {@link Serializable} variant of
     * {@link MethodParameter#getGenericParameterType()}.
     */
    @Nullable
    public static Type forMethodParameter(MethodParameter methodParameter)
    {
        return forTypeProvider(new MethodParameterTypeProvider(methodParameter));
    }

    /**
     * Unwrap the given type, effectively returning the original non-serializable type.
     *
     * @param type the type to unwrap
     * @return the original non-serializable type
     */
    @SuppressWarnings("unchecked")
    public static <T extends Type> T unwrap(T type)
    {
        Type unwrapped = type;
        while (unwrapped instanceof SerializableTypeProxy)
        {
            unwrapped = ((SerializableTypeProxy) type).getTypeProvider().getType();
        }
        return (unwrapped != null ? (T) unwrapped : type);
    }

    /**
     * Return a {@link Serializable} {@link Type} backed by a {@link TypeProvider} .
     * <p>If type artifacts are generally not serializable in the current runtime
     * environment, this delegate will simply return the original {@code Type} as-is.
     */
    @Nullable
    static Type forTypeProvider(TypeProvider provider)
    {
        Type providedType = provider.getType();
        if (providedType == null || providedType instanceof Serializable)
        {
            // No serializable type wrapping necessary (e.g. for java.lang.Class)
            return providedType;
        }
        if (GraalDetector.inImageCode() || !Serializable.class.isAssignableFrom(Class.class))
        {
            // Let's skip any wrapping attempts if types are generally not serializable in
            // the current runtime environment (even java.lang.Class itself, e.g. on Graal)
            return providedType;
        }

        // Obtain a serializable type proxy for the given provider...
        Type cached = cache.get(providedType);
        if (cached != null)
        {
            return cached;
        }
        for (Class<?> type : SUPPORTED_SERIALIZABLE_TYPES)
        {
            if (type.isInstance(providedType))
            {
                ClassLoader       classLoader = provider.getClass().getClassLoader();
                Class<?>[]        interfaces  = new Class<?>[]{type, SerializableTypeProxy.class, Serializable.class};
                InvocationHandler handler     = new TypeProxyInvocationHandler(provider);
                cached = (Type) Proxy.newProxyInstance(classLoader, interfaces, handler);
                cache.put(providedType, cached);
                return cached;
            }
        }
        throw new IllegalArgumentException("Unsupported Type class: " + providedType.getClass().getName());
    }


    /**
     * Additional interface implemented by the type proxy.
     */
    interface SerializableTypeProxy
    {

        /**
         * Return the underlying type provider.
         */
        TypeProvider getTypeProvider();
    }


    /**
     * A {@link Serializable} interface providing access to a {@link Type}.
     */
    @SuppressWarnings("serial")
    interface TypeProvider extends Serializable
    {

        /**
         * Return the (possibly non {@link Serializable}) {@link Type}.
         */
        @Nullable
        Type getType();

        /**
         * Return the source of the type, or {@code null} if not known.
         * <p>The default implementations returns {@code null}.
         */
        @Nullable
        default Object getSource()
        {
            return null;
        }
    }


    /**
     * {@link Serializable} {@link InvocationHandler} used by the proxied {@link Type}.
     * Provides serialization support and enhances any methods that return {@code Type}
     * or {@code Type[]}.
     */
    @SuppressWarnings("serial")
    private static class TypeProxyInvocationHandler implements InvocationHandler, Serializable
    {

        private final TypeProvider provider;

        public TypeProxyInvocationHandler(TypeProvider provider)
        {
            this.provider = provider;
        }

        @Override
        @Nullable
        public Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable
        {
            if (method.getName().equals("equals") && args != null)
            {
                Object other = args[0];
                // Unwrap proxies for speed
                if (other instanceof Type)
                {
                    other = unwrap((Type) other);
                }
                return ObjectUtils.nullSafeEquals(this.provider.getType(), other);
            }
            else if (method.getName().equals("hashCode"))
            {
                return ObjectUtils.nullSafeHashCode(this.provider.getType());
            }
            else if (method.getName().equals("getTypeProvider"))
            {
                return this.provider;
            }

            if (Type.class == method.getReturnType() && args == null)
            {
                return forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, -1));
            }
            else if (Type[].class == method.getReturnType() && args == null)
            {
                Type[] result = new Type[((Type[]) method.invoke(this.provider.getType())).length];
                for (int i = 0; i < result.length; i++)
                {
                    result[i] = forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, i));
                }
                return result;
            }

            try
            {
                return method.invoke(this.provider.getType(), args);
            }
            catch (InvocationTargetException ex)
            {
                throw ex.getTargetException();
            }
        }
    }


    /**
     * {@link TypeProvider} for {@link Type Types} obtained from a {@link Field}.
     */
    @SuppressWarnings("serial")
    static class FieldTypeProvider implements TypeProvider
    {

        private final String fieldName;

        private final Class<?> declaringClass;

        private transient Field field;

        public FieldTypeProvider(Field field)
        {
            this.fieldName = field.getName();
            this.declaringClass = field.getDeclaringClass();
            this.field = field;
        }

        @Override
        public Type getType()
        {
            return this.field.getGenericType();
        }

        @Override
        public Object getSource()
        {
            return this.field;
        }

        private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException
        {
            inputStream.defaultReadObject();
            try
            {
                this.field = this.declaringClass.getDeclaredField(this.fieldName);
            }
            catch (Throwable ex)
            {
                throw new IllegalStateException("Could not find original class structure", ex);
            }
        }
    }


    /**
     * {@link TypeProvider} for {@link Type Types} obtained from a {@link MethodParameter}.
     */
    @SuppressWarnings("serial")
    static class MethodParameterTypeProvider implements TypeProvider
    {

        @Nullable
        private final String methodName;

        private final Class<?>[] parameterTypes;

        private final Class<?> declaringClass;

        private final int parameterIndex;

        private transient MethodParameter methodParameter;

        public MethodParameterTypeProvider(MethodParameter methodParameter)
        {
            this.methodName = (methodParameter.getMethod() != null ? methodParameter.getMethod().getName() : null);
            this.parameterTypes = methodParameter.getExecutable().getParameterTypes();
            this.declaringClass = methodParameter.getDeclaringClass();
            this.parameterIndex = methodParameter.getParameterIndex();
            this.methodParameter = methodParameter;
        }

        @Override
        public Type getType()
        {
            return this.methodParameter.getGenericParameterType();
        }

        @Override
        public Object getSource()
        {
            return this.methodParameter;
        }

        private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException
        {
            inputStream.defaultReadObject();
            try
            {
                if (this.methodName != null)
                {
                    this.methodParameter = new MethodParameter(this.declaringClass.getDeclaredMethod(this.methodName, this.parameterTypes),
                            this.parameterIndex);
                }
                else
                {
                    this.methodParameter = new MethodParameter(this.declaringClass.getDeclaredConstructor(this.parameterTypes), this.parameterIndex);
                }
            }
            catch (Throwable ex)
            {
                throw new IllegalStateException("Could not find original class structure", ex);
            }
        }
    }


    /**
     * {@link TypeProvider} for {@link Type Types} obtained by invoking a no-arg method.
     */
    @SuppressWarnings("serial")
    static class MethodInvokeTypeProvider implements TypeProvider
    {

        private final TypeProvider provider;

        private final String methodName;

        private final Class<?> declaringClass;

        private final int index;

        private transient Method method;

        @Nullable
        private transient volatile Object result;

        public MethodInvokeTypeProvider(TypeProvider provider, Method method, int index)
        {
            this.provider = provider;
            this.methodName = method.getName();
            this.declaringClass = method.getDeclaringClass();
            this.index = index;
            this.method = method;
        }

        @Override
        @Nullable
        public Type getType()
        {
            Object result = this.result;
            if (result == null)
            {
                // Lazy invocation of the target method on the provided type
                result = ReflectionUtils.invokeMethod(this.method, this.provider.getType());
                // Cache the result for further calls to getType()
                this.result = result;
            }
            return (result instanceof Type[] ? ((Type[]) result)[this.index] : (Type) result);
        }

        @Override
        @Nullable
        public Object getSource()
        {
            return null;
        }

        private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException
        {
            inputStream.defaultReadObject();
            Method method = ReflectionUtils.findMethod(this.declaringClass, this.methodName);
            if (method == null)
            {
                throw new IllegalStateException("Cannot find method on deserialization: " + this.methodName);
            }
            if (method.getReturnType() != Type.class && method.getReturnType() != Type[].class)
            {
                throw new IllegalStateException("Invalid return type on deserialized method - needs to be Type or Type[]: " + method);
            }
            this.method = method;
        }
    }

}
